With the rapid development of the computer and electronic information industry and the appearance of vehicles and high-speed trains equipped with advanced electronic equipment in the 21st century, electromagnetic waves generated from various electronic products mutually influence electronic devices. For example, in some cases, the defects of the vehicle's electronic system in Japan, which were an international issue in early 2010, and the failure of the high-speed rail systems in Korea, were found to result from electromagnetic waves, and the electromagnetic waves may also cause loss of lives.
Moreover, there are a series of medical reports that electromagnetic waves directly cause serious harm to the human body. These electromagnetic waves are classified into high-frequency electromagnetic waves generated from various home appliances, such as mobile phone, radar, TV, and microwave, and low-frequency electromagnetic waves generated from household and industrial power generation, and particularly, electromagnetic waves generated at the high-frequency band of 100 MHz to several GHz cause harm to humans.
The unit to express the electromagnetic shielding effect is designated by decibel (dB), which means the electromagnetic intensity ratio before and after shielding. The effectiveness of 20 dB means the reduction in the amount of electromagnetic waves to 1/10, and the effectiveness of 40 dB means the reduction in the amount of electromagnetic waves to 1/100. It is generally determined that the shielding effect is favorable at 30-40 Db or more. In order to protect electronic devices and human bodies from the harm caused by the generation of electromagnetic waves, the regulations have been strengthened around the globe, and respective countries are strengthening EMI regulations.
Following this trend, a metal substrate is used, or a conductive coating or plating is applied to the substrate, for electromagnetic shielding. The metal substrate has disadvantages in that the processing of complicated patterns is difficult and it's heavy in weight. Moreover, the method of substrate plating is not advantageous in the productivity due to complicated processes therefor, such as degreasing, etching, neutralizing, activating, accelerating, metal depositing, activating, and primary to tertiary plating. Moreover, shielding materials using a filler, such as carbon nanotubes, a metal powder, graphite, or ferrite, have been reported, but they show defects in dispersibility, processability, electromagnetic shielding efficiency, and the like. Metal plating is applied to the filler in order to solve the disadvantages, but such a plating manner of a conductive powder is difficult for practical use due to a delicate process, productivity, and high production prices.
As for recent technologies associated with electromagnetic shielding, U.S. Pat. No. 5,827,997 discloses the complexation of nickel fibers, or carbon filaments plated with nickel through electroplating, with a polymer resin; US Publication No. 2002/0108699 discloses the complexation of conductive fibers with a resin; Korean Patent Application No. 10-2009-0031184 discloses an electromagnetic shielding film containing carbon nanotubes; Korean Patent Application No. 10-2006-0039465 discloses a method for manufacturing an electromagnetic shielding film; Korean Patent Application No. 10-2000-0039345 discloses an electromagnetic shielding material using carbon nanotubes or carbon nanofibers; and Korean Patent Application No. 10-2009-0057726 discloses a method for preparing a polymer/carbon nanotube composite with excellent electromagnetic shielding efficiency.
Throughout the entire specification, many papers and patent documents are referenced and their citations are represented. The disclosures of cited papers and patent documents are entirely incorporated by reference into the present specification, and the level of the technical field within which the present invention falls and details of the present invention are explained more clearly.